Installation standards, Table 2508.1
IBC Table 2508.1 names the standard for each gypsum product. Match the product to its pair:
- Gypsum panel products (gypsum board, wallboard): GA-216 or ASTM C840
- Gypsum sheathing: ASTM C1280 or GA-253
- Gypsum veneer base: ASTM C844
- Interior lathing and furring: ASTM C841
- Steel framing: ASTM C754 or ASTM C1007
The trap is the two paired lists. GA-216 and ASTM C840 go with wallboard; ASTM C1280 and GA-253 go with sheathing. Exterior gypsum sheathing behind cladding is installed per ASTM C1280 or GA-253, not GA-216. ASTM C926 is the exterior plaster standard referenced for weep screed installation, not a gypsum board standard.
Where wallboard is prohibited
IBC Section 2508.2 states gypsum wallboard shall not be used where there will be direct exposure to water or continuous high humidity. Gypsum wallboard or gypsum plaster also may not be used on exterior surfaces exposed directly to the weather.
That is the prohibition. The distractors are places wallboard is allowed:
- Fire-resistance-rated assemblies commonly use gypsum board; Section 2508.5 even sets joint treatment rules for them.
- Ceilings with framing at 24 in. o.c. are covered by GA-216 screw spacing, not prohibited.
- Level 1 finish is specifically suited to plenums and concealed areas under GA-214.
Joint treatment in rated assemblies
Under IBC Section 2508.5, fire-resistance-rated gypsum assemblies must have joints and fasteners treated unless one of five exceptions applies:
- A decorative finish equivalent to joint treatment
- Single-layer systems with joints located over wood framing
- Square-edge or tongue-and-groove (V-edge) board, backing board or sheathing
- Multilayer systems with the joints of adjacent layers offset
- Assemblies tested without joint treatment
The trap is the framing material. The single-layer exception covers joints over wood framing only. A single-layer system with joints over steel framing is not an exception, and those joints still need treatment. Joint treatment is required unless one of the five applies.